This invention relates to electrical circuit making and breaking devices. More particularly, it is concerned with electrical relays in which a buildup of static electricity is prevented from causing the contacts to become contaminated.
Reliable operation of electrical relays requires that an electrical circuit be completed each time relay contacts are brought together. The ability of the contacts to provide proper conduction is dependent upon their surfaces being free of nonconducting films or particles. The presence of nonconducting contaminating materials on the contact surfaces may result in random occurrences of contact discontinuity thereby adversely affecting the reliable operation of a relay.
Typically conventional relays include an insulating contact carrier on which movable contacts are mounted and an insulating support in which stationary contacts are mounted. The contact carrier moves reciprocally within the support causing the movable contacts to make and break electrical connections with the stationary contacts. The contact carrier, support, and other structural elements of the relay as well as the environment in which the relay operates are all possible sources of nonconducting contaminating materials. It has been observed that under operating conditions the reciprocally moving contact carrier very quickly becomes electrostatically charged and the movable contacts which are mounted on the contact carrier also acquire the electrostatic charge. Any dust, dirt, or particles of insulating material in the vicinity of the movable contacts are attracted to them. A film or layer of nonconducting contaminating material builds up on the surfaces of the movable contacts causing unreliable operation of the relay by making high resistance connections between the movable and stationary contacts.
Various techniques have been employed in attempting to overcome the problem of nonconducting contaminating materials at the contact surfaces. A wiping action between the contacts may take place as the contacts engage. Multiple contacts may be employed to provide redundant paths. The surfaces of the contacts may be made irregular as in a waffle pattern. A knife edge or pointed contact element which scores or pierces the contaminating materials may be employed. These mechanical techniques provide varying degrees of success under certain conditions; however, none completely avoids the problem of static electricity causing nonconducting materials to adhere to contact surfaces.